Electronic devices such as computers, personal digital assistants, and monitors typically have multiple power states. Two power states are “on”, when the device is operating at full power and “off”, when the device is turned off and not using any power. Another power state is “sleep” or “hibernate”, when the device is turned on but using less power than when in the “on” state. Sleep states are typically used to reduce energy consumption and to save battery life.
FIG. 1 is a right perspective view of a computer system according to the prior art. A user interacts with computer 100 and display 102 using keyboard 104. Button 106 may be used to turn on computer 100 or display 102, or it may be used to provide information to a user regarding a current power state of computer 100 or display 102. In the system shown in FIG. 1, button 106 is made of a transparent material that covers or overlays a light-emitting diode (LED). When computer 100 or display 102 is turned on, the LED emits light that transmits through button 106 and is seen by the user. When computer 102 enters the sleep state, the LED pulses to alert the user the computer is in the sleep state.
FIG. 2 is a data flow diagram for an LED signal in the computer system of FIG. 1. The data flow diagram includes waveform generator 200 and LED 202. Waveform generator 200 outputs a signal 204 that changes over time, which causes LED 202 to pulse. In some environments, such as dark rooms, the light emitted by LED 202 can be distracting or disruptive to the user.